Supernatants of spheroid cells promote tube formation of EPCs through VEGF up-regulation.

(A) Tube formation of EPCs treated by supernatants of spheroid cells was higher than their counterparts. And tube formation of EPCs was suppressed when we block the function of VEGF by bevacizumab. (B) The VEGF concentrations in supernatants of spheroid cells were higher than those of adherent cells. (C) Higher VEGF expression was observed in the spheroid cells compared with their counterparts.